Optical switching is expected to play an important role in future high capacity, for instance broadband, optical telecommunications networks. It is desirable to have all-optical switches in a communications network for several reasons, including the avoidance of a bit rate "bottleneck".
Optical switching can offer:
1. Large bandwidth. PA1 2. Avoidance of interfaces with electronics, thereby requiring less equipment than for instance electronic switching. PA1 3. No conversion to electrical form or re-shaping necessary. PA1 4. High switching speeds. PA1 5. Complex modulation schemes, coherent signals or packets of wavelengths can be switched without optical demultiplexing and multiplexing. PA1 6. Avoids discrepancies between optical transmission rates and electronic processing speeds. PA1 7. Potential for an optically transparent network (can accept a wide range of data rates). PA1 a) "Monolithically Integrated 2.times.2 InGaAsP/InP Laser Amplifier Gate Switch Arrays" by M. Janson et al, Proceedings of the 17th European Conference on Optical Communications, Post Deadline Papers, pp 28-30, PA1 b) GB Patent Application number 2227854A, in the name STC plc, published 8th Aug. 1990.
The semiconductor laser amplifier gate switch array is an attractive component, offering potential for zero insertion loss, polarisation insensitivity, low wavelength dependence, low crosstalk, high extinction ratio, high switching speed and simple drive conditions. Small size and scope for integration are both important criteria for the practical realisation of optical switches. Switches are known, including a 2.times.2 switch with waveguided Y-branched input and output, and a 2.times.2 switch in which the Y-branching is replaced by reactive ion etched (RIE) total internal reflection (TIR) mirrors instead of the waveguided Y-branching.
Known devices of the prior art which have relevance to the present invention are described in the following published documents:
The latter is entitled "Integrated Optics Asymmetric Y-Coupler" and provides a description of a fabrication technique for mirrors in optical semiconductor technology.